Display apparatus

ABSTRACT

A display apparatus has an interchangeable cassette including a first static image-bearing slatted panel and at least two further movable image-bearing slatted panels, movable relative to the static panel and interleaved therewith. The panels form part of the cassette in which any of the panels can be selectively removed and replaced. Additionally, the display apparatus includes a frame for receiving the cassette. The frame includes a drive system for selectively moving the movable panels to enable the slats on each of the movable panels to move from a position behind the slats of the static panel, to a position in front of the slats of the static panel, thereby enabling an image on the panels to be viewed.

BACKGROUND OF THE INVENTION

This invention relates to a display apparatus. In particular, it relatesto a display apparatus capable of sequentially displaying a plurality ofstatic images, such as advertising images.

Display apparatus of this type is extensively used in advertising,especially at the point of sale or on billboards for example. A typicalprior art example of an advertising medium capable of presenting morethan one image sequentially comprises an array of elongate elementswhich are triangular in cross-section. Parts of the whole image areprovided on each of the elongate faces so that when one set of theseface outward a viewer can see an entire image disposed across all thefaces. After a time period, each of the element rotates about itslongitudinal axis to bring another face forward to view a second image.Such a system therefore enables three different images to be viewed,each for a predetermined period of time.

Such devices are, however, bulky and have a large depth because of thedepth required by the triangular section pieces. Also, sinceadvertisements are changed and updated regularly, it can be difficult tochange an advertisement since this requires altering the image on eachof the three faces on each of the triangular pieces. This can be verytime consuming where a large number of triangular pieces are provided toform each image. For example, twenty separate triangular pieces may belaid continuously to form a single image.

Attempts have been made to reduce the complexity of such devices and toovercome the complexity of rotating members by using planar sheets.Examples of these are shown in U.S. Pat. Nos. 2,141,393, 3,403,465,3,421,240 and 3,659,367. Each of these relates to a changeable displaystructure comprising a plurality of slatted sheets which are interleavedsuch that relative sliding movement causes images to be selectivelyexposed to view. Often, as in U.S. Pat. Nos. 2,141,398 and 3,659,367these devices are intended for manual manipulation and are therefore oflimited use. Attempts to drive the sheets, by means such as motors, haveoften tended to complicate their structure, as in U.S. Pat. No.3,421,240. Also, in prior art devices it has generally been difficult ortime consuming to change messages. Training, and therefore skilledpersonnel, is often required to change the messages displayed.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved displaymeans which enables the messages displayed to be easily and simplychanged by unskilled personnel in a short amount of time.

According to the present invention there is provided a display apparatuscomprising an interchangeable cassette including a first staticimage-bearing slatted panel, at least two further image-bearing slattedpanels, each movable relative to the first slatted panel and interleavedtherewith, the three or more slatted sheets forming part of a cassettein which any of the sheets can be selectively removed and replaced, anda frame for receiving the cassette comprising a drive means having meansfor selectively moving the sheets other than the first one to enable theslats on each of the movable sheets to move from a position behind theslats of the first sheet, to a position in front of the slats of thefirst sheet, to thereby enable the image on the sheet to be viewed.

Preferably the frame includes the drive means on a rear portion thereof.A front frame portion may be provided which can detachably connect tothe cassette to detachably secure the cassette within the frame. Thecassette may alternatively or in addition be located by one or more pinsand cooperating locating holes and sockets on the frame and cassette.

Preferably, the drive means comprises a plurality of pins driven bymeans such as solenoids and the moveable sneers comprise holes andslots, the holes in one sheet being in register with the slots of othersheets such that each pin can enter a hole in one sheet only to moveonly that sheet, the pin moving within the slots of the other sheets sothat these sheets are not moved by that pin.

The drive means may also be operated and controlled remotely. The devicemay be used as a trilingual (or more) directional sign for example.

According to the present invention there is further provided a removablecassette for a display apparatus, comprising a front panel, a rearpanel, a static image-bearing slatted panel and at least oneimage-bearing slatted panel, movable with respect to the static paneland interleaved therewith, the image-bearing panels being sandwichedbetween the front and rear panels.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 shows a front panel of a cassette;

FIG. 2 shows a rear panel of a cassette;

FIGS. 3, 4, 5 and 6 show slatted sheets forming part of a cassette andbearing respective first to fourth images;

FIG. 7 shows how the slatted sheets of FIGS. 3 to 6 are interassembled;

FIG. 8 shows a sequence in which the sheets may be relatively moved topresent different images to a viewer;

FIG. 9 shows an exploded schematic view of a display apparatus;

FIG. 10 shows at (a), (b) and (c) respective top, side and front viewsof a driving mechanism;

FIG. 11 shows an enlarged detail of part of FIG. 10(c);

FIGS. 12 and 13 show timing diagrams;

FIG. 14 shows the functioning of a latching finger; and

FIG. 15 shows a latching finger.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the Figures, a display apparatus comprises a frame having arear panel and a front panel. A removable exchangeable cassette can beplaced within the frame, which cassette comprises means for displaying arespective series of images. These may be advertising images and theapparatus may be placed at a point of sale for example.

An interchangeable cassette comprises a rear panel 50 (FIG. 2), three ormore image bearing panels (of which four are shown in FIGS. 3 to 6) anda front panel 23 (FIG. 1) bearing a window 22 through which respectiveimages of the image panels may be seen.

The image bearing panels comprise a first static panel shown in FIG. 3.This panel 1 is formed from a thin sheet of a material such as aplastic, paper or board material which is cut to form a plurality ofparallel slats 2. An image is formed across the slats so that whenviewed from the front the image appears to be complete. In FIG. 1, theimage is a large 0 (zero). More typically, the image would of course beadvertising or other material. The shaded area of the image plates showsthe area of the plate viewed through the window of the front plate. Inthis example, twenty slatted portions are provided. Six through-holes 3are formed in the upper and lower parts of the sheet, which act aslocating holes for fitting over pins on the back panel of the cassette.A plurality of slots 4 are also provided at each end of the sheet. Thenumber of slots is dependent on the number of images which are to beportrayed by the cassette. In the example shown, four images areportrayed and therefore three slots are provided at each end. If morethan three are to be portrayed, say n images, then n-1 slots will needto be provided at each end of sheet 1. Alternatively, only two or moremovable sheets may be provided.

FIGS. 4 to 6 show second, third and fourth sheets, respectively formingpart of the cassette bearing images 1, 2 and 3, respectively. These aremovable sheets which slide relative to static sheet 1 to present theirrespective images in front of the image shown by sheet 1. Each of themovable sheets has a plurality (for example twenty) of slatted portions7₁, 7₂, 7₃. These are each formed by making a plurality of cuts 9parallel to the sides of the sheets and further cuts 10, 11 from the topand bottom of each cut 9. Each movable panel comprises through holes 14,14, 15, 15, 8, 8 at each edge for receiving a driving pin to move therespective sheet back and forth with respect to static sheet 1. One ortwo slots 16 are also provided at each end of each panel, the slots ofone panel being positioned so that when the sheets are laid over oneanother a slot from one sheet lays substantially over the whole of asecond panel and vice-versa so that the pin which is received in, say,hole 14 of the first panel moves within the slot 16 of the second andthird panels so that when this pin is actuated only the first panel 5and not the other panels move. Similar holes and slots are formed in theother respective side of each panel.

Clearly, if more or less than three movable panels are provided thenthere will need to be an increased or decreased number of slots in eachpanel to accommodate the additional or lesser number of pins necessary.

Further locating slots 18 are provided towards the top and bottom ofeach of the movable panels through which the locating pins which locateinto holes 3 in sheet 1 can protrude. The slots also limit lateralmovement, ensuring that the slats remain engaged and do not separatethrough over-travel. Clearly, in the movable panels these must be slotsrather than holes since the panels are movable and space must thereforebe allowed for relative movement of the panel and pin. An additionalcassette location hole is shown at 19 in each of FIGS. 1 to 6. In thefront, rear and static image panels this is a hole while in the movablepanels it is of course a slot

FIG. 7 shows schematically the interconnection of static panel 1 and themovable panels. In this figure, a number of adjacent slats of each panelare shown. As is shown in the figure, the slats of layer 0 lie at suchan angle to each other that the slats of layers 1, 2 and 3 can liebetween adjacent slats of layer 0. Layer 1, 2 and 3 are then slidablymoved back and forth with respect to layer 0 to bring the image on,respectively, layer 1, layer 2 or layer 3 in front of the image of layer1 to display that image. Layer 1 is mounted underlying layer 0, layer 2underlies layer 1 and layer 3 underlies layer 2. Clearly, if anadditional movable panel is to be provided, then the slat angles willneed to be greater to accommodate the extra depth required betweenadjacent slats. Alternative, less movable panels will need a smallerangle. More than three movable panels may be provided, but the angles ofthe slats start to become so large that the image becomes distorted. Tominimize this effect, the panels are of a thin material in proportion tothe size of the graphics being displayed. Also, distortion effects maybe overcome by increasing the slat width, thus reducing the layeringangle effect.

The sheets forming the image panels are preferably of a flexiblematerial, and may for example be paper encapsulated in a plastic (e.g.polypropylene) layer. Polypropylene has a low co-efficient of friction,this aids the sliding movement of the panels. Other plastic materialsmay be used. This may, e.g., be heat shrunk onto the paper. The sheetsmay be, for example about 200-250 μm in thickness. The sheets aretherefore too thin to have inherent mechanical stability. The stabilityof the slatted material is achieved in the present invention by thesandwiching effect between the front and back panels of the cassette,enabling the moving panels to slide and preventing them from twistingand becoming disengaged. The front and back panels are therefore of arigid or relatively rigid material.

To ensure that the slats do not stick or become disengaged when slidbackwards and forwards, a degree of overlap is required as shown at 20.The slats of layers 1, 2 and 3 overlap the respective slats of layer 0by around 5% of their width. Although this does mean that 5% of theimage displayed by panel 1 will be obscured, in practice this isinsignificant and the overall image quality is not unduly visiblydeteriorated. Also, it is desirable to displace the movable panels bydifferent amounts. Thus, layer 7 is displaced by, say, 5% of its slatwidth less than layers 2 and 3 from its obscured to its visibleposition. This is shown at 21 which shows the maximum position to whichthe two panels move. For example, Layer 1 may move by 18 mm each stroke,while layers 2 and 3 move by 19 mm.

FIG. 8 shows schematically the sequence in which the panels are moved.The figure shows two adjacent interleaved slats of 4 panels. At a firstpoint in time the slats of the movable layers 1, 2 and 3 are obscuredbehind the slats of static layer 0. Thus, the image on layer 0 isviewed.

Movable panel 1 then moves in front of layer 0. Layer 2 is then movedbehind layer 1 (step 3). After layer 1 has been viewed for apredetermined time it is retracted (step 4) revealing layer 2. Layer 3is then moved behind layer 2 (step 5). After layer 2 has been viewed fora selected time, it is retracted (step 6), revealing layer 3. Finally,again after a selected time internal layer 3 is retracted and step 1 isreached again. The cycle then repeats.

It is found desirable to move layers into position while the image onthe previous layer is still being viewed to ensure the smoothestpossible changeover and to even out the distribution of powerconsumption. This reduces the load on the solenoid or other drive-motorscaused by excessive power at start-up.

Preferably, the timing is programmable so that the time for which theimage on layers 0, 1, 2 and 3 are viewed may differ between each panel.This could be useful if one of the panels bears a message containing alot of text for example which takes more time to read and to absorb thanthe other images. Also by making a very quick transition between two ormore of the images, a degree of animation can be achieved. This has theadvantage of attracting a potential viewer, as sensations of movementare sensed by central or peripheral vision, drawing the viewer to thedisplay.

FIG. 1 shows the front panel 23 of the cassette which incorporates theimage panels. The front panel comprises window 22 through which therespective images can be viewed. The window may be of optically polishedglass, or a transparent plastic material for example. The frame may beof polycarbonate. The front panel 23 also includes slots 24 at eachside, corresponding with the slots such as 16 and through which thedriving pins may move. Frame 23 may also include a peripheral locatingflange 25 for locating the image panels, as does rear panel 50.

Thus, in use, an interchangeable cassette comprises a rear panel, thefour interleaved slatted flexible layer 0 to 3 and a front panel. Thefront and rear panels are spaced apart by pins such as 51 extending fromthe rear panel, through holes or slots 18 in the flexible panels andinto corresponding blind holes 52 in the front panel.

As shown in FIG. 9, the display cassette (including the rear panel 50,the flexible, slatted image display panels and the front window frame23) are sandwiched in use between a rear drive panel 30 and a frontframe portion 31. Driving pins such as pins 32,33 on the drive unit 30locate into holes 14, 15 and 8 and through the slots on the remainingpanels of the cassette to enable the driven panels to be so driven. Thecassette is also located by location pins protruding from rear drive and30 through hole 19. Thus, it is an easy matter to remove and replace acassette. The front and back panels may be hinged together so that thefront hingeably opens to insert or remove a cassette. Otherconfigurations may be used.

FIG. 10(a) shows a drive mechanism.

Driving is achieved by respective pins 32, 33, 34, 132, 133, 134 whichact upon holes 14, 15 and 8 in lines 1, 2 and 3 to move these layerssidewardly. Each pair of pins acts upon a particular layer to move thislayer relatively to the other layer. Each associated pair of pins, e.g.32 and 132 is powered by a drive means connected to two magneticallylatched solenoids 38 and 39. Other types of drive means may of course beused. Pin 32 is connected by a rod to solenoid 38 and pin 132 isconnected by a rod to solenoid 39. The drives from the solenoid arelinked to thereby connect pins 32 and 132 together to thereby shift thepins together. The mechanism of the solenoids is described furtherbelow. When solenoid 33 drives rod 37 to the left in the figure then 32moves its respective flexible image layer leftwardly. Rod 40 is alsodrawn to the left and thereby pin 132 also moves leftwardly. Whensolenoid 39 is actuated it drives rod 40 and thereby pin 132 to theright and brings with it rod 37 and pine 32. Similarly, pins 33, 133 andpins 34, 134 are driven by respective solenoid pairs at different timesdetermined by a timing circuit to move the other layers. Timing circuitsare well known and will not be described further.

In an alternative embodiment, the solenoids may be remote from theapparatus and connected by, for example, a cable.

Each of the rods such as 37 and 40 are guided by a plurality of rollers41. The movement of the respective pins is limited by springs 42 andplates 43 to ensure that their movement stops before the end of a rodhits the end of the solenoid, to reduce noise and avoid the clunk thatwould otherwise occur as the rod hits the back of the solenoid at speed.Furthermore, dampers are preferably provided (as shown in FIG. 10(c) andin more detail in FIG. 11). Additionally, a protrusion 44 on each one ofthe respective rods is connected to a fixed point 45 by a spring 46.Thus, the spring connected to each of an opposing pair of rods, such asrods 37 and 40 oppose one another. These springs act as counterbalanceswhen the cassette is used in portrait mode to counter gravitationalforces.

FIG. 10(c) shows a side view of FIG. 10(a) to illustrate the drivingmechanism in a little more detail and FIG. 10(b) shows a front view.

Referring to FIG. 10(b) an embodiment is shown in which a front panel ofthe apparatus 31 is connected to back panel 30 by a hinge 50. A cassette53 is shown in dashed lines as partially emerging from the frame. Inorder to assist in detaching the cassette when the assembly is opened, acassette detaching member 151 as shown in FIG. 10(a) is at a portionwhich extends under the cassette assembly and an enlarged end portion,having apertures to accommodate the driving pins and which restsunderneath the top part of the assembly 31 at a position where thisextends beyond the extent of the cassette. The member is hinged 151 andbiased so that as top part 31 is lifted upwards member 151 moves fromits base position shown in solid lines in FIG. 10(b) to its upperposition shown in dashed lines. This in turn pushes upon the cassette 53and causes it to disengage from the pins and to be pushed up asufficient distance so that it can easily be manually removed. Member151 also therefore acts to protect the driving pins when a cassette isremoved. A mechanism 151 is preferably present at each end of theassembly to protect both sets of pins.

FIG. 11 shows an enlarged part of FIG. 10(c). The magnetically latchedsolenoid assembly for each rod comprises a solenoid 160 and a permanentmagnetic 161. The rod 40 extends through permanent magnetic 161 and coil160. The situation shown in FIG. 11 is when the right hand solenoid isenergized to move rod 40 to the right. Since the other solenoid 38 isdeenergised, the rod on this side is pulled to the right by acombination of the magnetic field of permanent magnetic 161 and theforce of solenoid 39, together with the various spring forces. Thus, thestop 43 associated with solenoid 38 is abutted against permanentmagnetic 161 in the figure and the spring 42 is not seen since this issurrounded by stop 43. The rods 37 and 40 are connected through a damper43. This damps the ends of the movement to ensure that the movements,although swift, are smooth and that there is not a sudden jolt at theend of each rods movement. These dampers are similar to those whichmight be used on, for example, motor drives of video cassette players.Essentially, an oil damped cam 162 is constrained to move between twotransverse limiting rods 163 and 164, the cam being acted upon by theends of rods 37 and 40 and transmitting motion between them. The rodsare spaced apart to give the required stroke for each image plate, e.g.18 or 19 mm. A separate damper is used for each pair of associated rods.FIG. 11 shows, mounted underneath the solenoids and damper assembly, aprinted circuit board 165 bearing the circuitry for the system.

It will be appreciated that the mechanism may either be usedhorizontally (landscape mode), as shown, or may be used vertically(portrait mode) so that the rods and pins move in a generally verticaldirection. The springs 46 then act as counterbalances.

A secondary display may be driven through an electronic signal betweenthe master display and the secondary, slave, display. Thus, a secondaryslave display may be driven in an alternating sequence so that two, orindeed more, displays may be placed adjacent to each other, back to backor at right angles for example to provide a series of images displayedside by side or adjacently.

The solenoids are actuated by a programmable controller timer, typicallya programmable integrated circuit, such as a microprocessor, which canactuate each solenoid independently to control the time at which eachpanel is moved backwards and then forwards. In one embodiment, thetiming may be actuated by two adjacent micro switches or other switchingdevices. These are shown at 166 in FIG. 10(a). A combination ofdifferent timing selections can be made corresponding to which microswitches is actuated. Each layer of the cassette, except one layer(typically the static image layer), is then provided with two holes orslots in register with the switches through which the microswitches canprotrude. The remaining layer (e.g. the static layer) is used to`program` the microswitch circuit by either having one, two or no holes167 (FIG. 3). If two holes are present in this layer then no microswitchis set. If one hole is present then a respective correspondingmicroswitch is set and if two holes are present then both microswitchesare set. Timing programs can be pre-programmed which are different foreach combination. Thus, a cassette can be pre-programmed to beassociated with a certain timing program. A second cassette might beassociated with a different timing program and insertion of thatcassette automatically sets up the timing program. This has asignificant advantage that each cassette automatically sets up its owntiming program and no additional user input or programming is required.Alternative methods of achieving this will be apparent. Morecombinations may be achieved by providing more switching and hole/slots.

FIGS. 12 and 13 illustrate the various time periods above graphically.Layer 1 for instance is exposed for its image to be viewed over timeperiod T₁. The solid marks indicate when the various solenoids (Solenoid1 . . . Solenoid 6) driving the panels are actuated. Layer 2 is exposedduring period T₂ and layer 3 is exposed during period T₃ and duringperiod T₄ the static layer 0 is exposed.

In FIG. 12, four different timing routines are shown, set by thecassette as described above. The example shown in FIG. 13 is one ofthese timing routines. In mode A no timing holes are provided in layer0. The units of FIG. 12 are seconds.

The hollow marks of FIG. 3 indicate when the solenoids of an optionalslave display are actuated, to enable more than one changeable displayto be used and minimise power dissipation.

Advantageously, window panel 23 is provided with a finger portion 7 onits underside, as shown in FIG. 7. This portion is elongate and has oneend 75 fixed to (or integral with the panel 23. The remainder of thefinger tends to hang from the panel, as shown in FIG. 9. Finger 71includes a hinge portion 76 between its ends and a downwardly extendingportion 77 at its distal end.

Finger 71 acts to ensure that all the panels can have a fixed parkingportion from where the display cycle starts, or for use during transitof the cassette. For this purpose, additional slots 73 are provided inthe respective display panels 5 and 6, and additional holes 72 and 79are provided respectively in rear cassette panel 50 and static displaypanel. The hole in the static display panel is laterally extended asshown. When the panels are interconnected, the distal end of finger 71drops and protrusion 77 locates within slots or holes 72, 73 and 79,each of which has a laterally extended portion 80 for receivingprotrusion 76. This sets the respective positions of the panels andprecludes relative movement. It is therefore of particular benefit ifthe cassette is used vertically (i.e. in a `portrait` disposition). Whenthe cassette is attached to a frame, and the drive means are actuated apin 81 connected to the rear frame or drive pushes protrusion 77, andthereby finger 71 into an upward position, thereby pushing protrusion 76out of slots/holes 72, 73, and 79 to free it therefrom. Lateral movementof panels 5 and 6 is then enabled since pin 81 can slide in slots 73 and74. When pin 81 is retracted, finger 71 drops resiliently into its`locking` position, thus locking the panel in a parked position. Thefinger remains in this position when a cassette is removed for transit.In addition, a further microswitch may be actuated by finger 151 (FIG.10(b)) when a cassette is removed, which energises the solenoids to moveall the panels into the park position.

FIG. 14 also indicates an extrusion 200 joining the edges of the frontand back panels of a cassette, and illustrates the image layerssandwiched between them.

Alternatively, the unit may be controlled remotely in order to provide ameans of selecting a desired message or advertisement for example duringa given period of time.

What is claimed is:
 1. A display apparatus comprising:an interchangeablecassette, the cassette including a front cassette panel, a rear cassettepanel which directly engages the front cassette panel and is affixedthereto, a first static image-bearing slatted panel having a pluralityof slats, and at least two movable image-bearing slatted panels, havinga plurality of slats, each movable panel movable relative to the firststatic panel, the static panel and the movable panels forming part ofthe cassette and being positioned between the front cassette panel andthe rear cassette panel, and a frame for receiving the cassette, theframe comprising a drive means for selectively moving the movable panelsto enable the slats of the movable panels to move from a position behindthe slats of the static panel, to a position in front of the slats ofthe static panel, to thereby enable an image on the movable panels to beviewed, wherein the slats of the static panel are interleaved with theslats of the movable panels.
 2. The display apparatus as claimed inclaim 1 wherein the drive means are provided on a rear portion of theframe.
 3. The display apparatus as claimed in claim 1 wherein the drivemeans comprises a plurality of drive pins and wherein the movable panelsfurther comprise a plurality of holes and slots, the holes in one ofsaid movable panels being in register with the slots of another of saidmovable panels so that one of said drive pins can simultaneously enterone of said holes in the one of said movable panels, to move only theone of said movable panels, and move within the slots of the other ofsaid movable panels, so that the other of said movable panels are notmoved by the one of said drive pins.
 4. The display apparatus as claimedin claim 3 wherein the plurality of holes includes two driving holestowards opposing ends of each of said movable panels, and the pluralityof drive pins includes a pair of driving pins for each of said movablepanels, wherein each of said driving holes is driven by a respectivedriving pin, and wherein each of said pair of driving pins is driven byan opposing pair of magnetically latched solenoids in substantiallyopposite directions.
 5. The display apparatus as claimed in claim 4wherein each of said opposing pair of solenoids is associated withresilient means such that as a solenoid in each said pair is energizedto move an associated pin in a direction, another solenoid of said pairis biased by the resilient means to move another associated pin in thesame direction.
 6. The display apparatus as claimed in claim 3 furthercomprising at least one resiliently-biased means for partially removingthe cassette when the frame is open and simultaneously protecting thedrive pins.
 7. The display apparatus as claimed in claim 1 wherein eachof the slatted panels is a flexible sheet.
 8. The display apparatus asclaimed in claim 7 wherein the slatted panels are of thickness 200-250μm.
 9. The display apparatus as claimed in claim 1 further includingtiming means for actuating the drive means for different panels atpredetermined time intervals.
 10. The display apparatus as claimed inclaim 9 wherein the cassette further comprises means for automaticallyprogramming the timing means when the cassette is inserted into theframe.
 11. The display apparatus as claimed in claim 1 wherein amovement stroke of at least one of the said movable panels is differentfrom that of the other said movable panels.
 12. The display apparatus asclaimed in claim 1 wherein the slats of the movable panels partiallyoverlap the slats of the static panel at rest.
 13. The display apparatusas claimed in claim 1 wherein movement of the panels is such that afirst movable panel moves to reveal an image on the first movable panel,a second movable panel moves substantially behind the first movablepanel and the first movable panel then retracts to reveal an image onthe second movable panel, these steps being repeated for all the movablepanels.
 14. The display apparatus as claimed in claim 1 furtherincluding counterbalancing means for countering gravity when theapparatus is used in a vertical disposition.
 15. The display apparatusaccording to claim 1 wherein any of the static or movable panels can beselectively removed and replaced.
 16. The display apparatus as claimedin claim 1 wherein the cassette is removable from the frame withoutdisassembling the cassette.
 17. The display apparatus as claimed inclaim 1 wherein the cassette assembly is detachable and reattachablefrom the drive means of the frame.
 18. The display apparatus as claimedin claim 1 wherein the static panel and the movable panels form part ofthe cassette in which any of the static or movable panels can beselectively removed and replaced.
 19. A display apparatus comprising:aninterchangeable cassette, the cassette including a first staticimage-bearing slatted panel having a plurality of slats, and at leasttwo movable image-bearing slatted panels, having a plurality of slats,each movable panel movable relative to the first static panel, thestatic panel and the movable panels forming part of the cassette inwhich any of the static or movable panels can be selectively removed andreplaced, a frame for receiving the cassette, the frame comprising adrive means for selectively moving the movable panels to enable theslats of the movable panels to move from a position behind the slats ofthe static panel, to a position in front of the slats of the staticpanel, to thereby enable an image on the movable panels to be viewed,and timing means for actuating the drive means for different panels atpredetermined time intervals, wherein the slats of the static panel areinterleaved with the slats of the movable panels, wherein the cassettefurther comprises means for automatically programming the timing meanswhen the cassette is inserted into the frame, wherein the programmingmeans comprises the presence or absence of switch actuators on thecassette and a corresponding switch means on the frame connected to thetiming means.
 20. The display apparatus as claimed in claim 19 whereinthe programming means comprises two or more switches and two or morepositions where through-holes are selectably present or absent in thecassette to respectively actuate or not actuate the switches, andwherein different settings of the switches correspond to differenttiming programs.
 21. A display apparatus comprising:an interchangeablecassette, the cassette including a first static image-bearing slattedpanel having a plurality of slats, and at least two movableimage-bearing slatted panels, having a plurality of slats, each movablepanel movable relative to the first static panel, the static panel andthe movable panels forming part of the cassette in which any of thestatic or movable panels can be selectively removed and replaced, and aframe for receiving the cassette, the frame comprising a drive means forselectively moving the movable panels to enable the slats of the movablepanels to move from a position behind the slats of the static panel, toa position in front of the slats of the static panel, to thereby enablean image on the movable panels to be viewed, wherein the slats of thestatic panel are interleaved with the slats of the movable panels,wherein the cassette further comprises a latching means for latching thepanels of the cassette when parked or when the cassette is removed fromthe frame, the latching means comprising a latching element which ismoved out of a latching position, against a resilient return force, by apart of the frame when the cassette is inserted, but resiliently returnsto the latching position when the cassette is removed.
 22. The displayapparatus as claimed in claim 21 wherein the latching element is aresilient finger, movable in a series of registered slots in the panels.23. A display apparatus comprising:an interchangeable cassette, thecassette including a first static image-bearing slatted panel, having aplurality of slats, and at least two movable image-bearing slattedpanels having a plurality of slats, each movable panel movable relativeto the first static panel, and a frame for receiving the cassette, theframe comprising a drive means for selectively moving the movable panelsto enable the slats of the movable panels to move from a position behindthe slats of the static panel, to a position in front of the slats ofthe static panel, to thereby enable an image on the movable panels to beviewed, wherein the slats of the static panel are interleaved with theslats of the movable panels, wherein the drive means comprises aplurality of drive pins and wherein the movable panels further comprisea plurality of holes and slots, the holes in one of said movable panelsbeing in register with the slots of another of said movable panels, sothat one of said drive pins can simultaneously enter one of said holesin the one of said movable panels, to move only the one of said movablepanels, and move within the slots of the other of said movable panels,so that the other of said movable panels are not moved by the one ofsaid drive pins, wherein the plurality of holes includes two drivingholes towards opposing ends of each of said movable panels, and theplurality of drive pins includes a pair of driving pins for each of saidmovable panels, wherein each of said driving holes is driven by arespective driving pin, and wherein each of said pair of driving pins isdriven by an opposing pair of magnetically latched solenoids insubstantially opposite directions, and wherein each of said opposingpair of solenoids is associated with resilient means such that as asolenoid in each said pair is energized to move an associated pin in adirection, another solenoid of said pair is biased by the resilientmeans to move another associated pin in the same direction.
 24. Thedisplay apparatus of claim 23, wherein each of the slatted panels is aflexible sheet.
 25. The display apparatus of claim 24 wherein theslatted panels are of thickness 200-250 μm.
 26. A display apparatuscomprising:an interchangeable cassette, the cassette including a firststatic image-bearing slatted panel, having a plurality of slats, and atleast two movable image-bearing slatted panels, having a plurality ofslats, each movable panel movable relative to the first static panel,and a frame for receiving the cassette, the frame comprising a drivemeans for selectively moving the movable panels to enable the slats ofthe movable panels to move from a position behind the slats of thestatic panel, to a position in front of the slats of the static panel,to thereby enable an image on the movable panels to be viewed, whereinthe slats of the static panel are interleaved with the slats of themovable panels, wherein the drive means comprises a plurality of drivepins and wherein the movable panels further comprise a plurality ofholes and slots, the holes in one of said movable panels being inregister with the slots of another of said movable panels, so that oneof said drive pins can simultaneously enter one of said holes in the oneof said movable panels, to move only the one of said movable panels, andmove within the slots of the other of said movable panels, so that theother of said movable panels are not moved by the one of said drivepins, wherein the display apparatus further includes at least oneresiliently-biased means for partially removing the cassette when theframe is open and simultaneously protecting the drive pins.